code: def check_backward(self, x_data, y_grad):
      gradient_check.check_backward(
          LowerTriangularMatrix(), x_data, y_grad, eps=1e-2, rtol=1e-2
      )
  
file_path: chainerrl/tests/functions_tests/test_lower_triangular_matrix.py
imports: import unittest
  import numpy
  import chainer
  from chainer import cuda
  from chainer import gradient_check
  from chainer import testing
  from chainer.testing import attr
  from chainerrl.functions.lower_triangular_matrix import lower_triangular_matrix
  from chainerrl.functions.lower_triangular_matrix import LowerTriangularMatrix
label_desc: Use image node_id 5 for calling the TestLowerTriangularMatrix obj's underlying member method code with example usage: obj.check_backward(x_data, y_grad) without return types